1. Field of Invention
The present invention relates to a fastening structure and, in particular, to a fastening structure for the purpose of fastening an attaching member to an attached member with a fastening device used for this purpose.
2. Background Art
The fastening device of this kind such as for example a bolt and the like has so far been known to be used for fastening the attaching member to the attached member. The fastening device is generally designed to be firmly coupled with the attaching and attached members and by no means intended to be removed from the attaching and attached members to ensure that the fastening device functions to be an anti-theft device for protecting the attaching and attached members from theft. Many kinds of fastening devices as such anti-theft devices for protecting the attaching and attached members from theft have so far been employed in various fields.
For example, one of the typical examples now employed is raised an automatic transmission apparatus used for an automotive vehicle or a power transmission apparatus used for a hybrid automotive vehicle which is operated with an electric motor and an internal combustion engine as a prime mover. The power transmission apparatus is designed to electrically detect the operation of a shift lever or a shift switch for controlling range shifting means with an actuator capable of being electrically controlled. The control system of the power transmission apparatus thus constructed is called a shift-by-wire (hereinafter simply referred to as a “SBW”) and adapted for changing a mechanical operating linkage into an electrical operating system, thereby giving rise to enhanced freedom to the operation method for operating a shift operation section and the arrangement of parts and elements to be operated for performing the shift operation.
In the power transmission apparatus is provided a parking lock mechanism, which is designed to mechanically lock one of the rotating members arranged in a power transmission path from an engine to drive wheels when the shift lever is shifted to a parking range.
The above power transmission apparatus of this kind is known to comprise a locking pawl of a swingable type that serves to selectively engage with and disengage from one of the rotating members arranged in the power transmission path from the engine to the drive wheels and lock the rotating member when the shift lever is shifted to the parking range, a linear motion cam for swingably operating the locking pawl, an operation link for advancing and retracting the linear motion cam, and an SBW motor for rotating the operation link (see JP-3692791).
The parking lock mechanism is constructed to allow the lock pawl to be brought into engagement with the rotating member, thereby regulating the rotations of the rotating members forming the power transmission mechanism such as gears, chains, and shafts coupled to drive wheels. This results in the fact that the vehicle cannot be moved, thereby preventing the vehicle from being stolen.
However, in the case that the SBW motor, i.e., an actuator externally mounted on the case of the power transmission apparatus equipped with the parking lock mechanism is removed from the case, there is a possibility that the vehicle is stolen since the vehicle can be moved if the lock pawl of a swingable type to be brought out of engagement from the rotating member by tampering the parking lock mechanism.
In order to prevent the actuator from being removed from the case, the actuator and the case are considered to be firmly secured with each other using an anti-theft bolt described above.
As one of the anti-theft bolts is known a bolt 235 shown in FIG. 20 and comprising a threaded portion 231 screwed into a threaded groove formed in the attached member through a through bore formed in the attaching member, an umbrella-like slant portion 232 formed on the threaded portion 231, and an engagement portion 234 integrally connected to the umbrella-like slant portion 232 through a torsion portion 233 and having an outer peripheral portion to be engaged with a hexagonal wrench (for example, see JP-A-2003-90173).
In the case that the case of the power transmission apparatus is attached with the actuator with the bolt 235, the engagement portion 234 is engaged with a tool to have the threaded portion 231 screwed into the threaded groove, and then the torsion portion 233 is twisted and forcibly cut off to make the engagement portion 234 be separated from the umbrella-like slant portion 232, thereby making it possible to expose to the outside the umbrella-like slant portion 232 which cannot be engaged with the tool.
The bolt thus constructed is utilized to firmly engage the actuator with the case of the power transmission apparatus to make it possible for the bolt to be prevented from being removed from the case as well as to make it possible for the vehicle to be prevented from being stolen by the parking lock mechanism being tampered from the outside.
In lieu of the previously mentioned bolt 235 having a construction thus explained, a one-way bolt having an engagement portion to be engaged with a tool in only one direction to have the bolt clamped down is considered to be utilized. In this case, the bolt cannot be removed from the case when the actuator is firmly attached to the power transmission apparatus (for example, see JP-A-2001-207705).